The present invention relates to a process for providing a bonded composite product by the deposition of a coating of pyrolytic carbon on the exposed surfaces of a laminate including at least one porous carbon substrate and particles of a thermally stable solid and which contains a relatively less porous carbon substrate also in contact with the particles. In particular, the present invention relates to the use of a carbonizable gas which contacts the heated laminate so that pyrolytic carbon coating deposits on the laminate surfaces to produce bonding.